4.20-stable review patch. If anyone has any objections, please let me know.
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From: Dominique Martinet dominique.martinet@cea.fr
commit 574d356b7a02c7e1b01a1d9cba8a26b3c2888f45 upstream.
If the requested msize is too small (either from command line argument or from the server version reply), we won't get any work done. If it's *really* too small, nothing will work, and this got caught by syzbot recently (on a new kmem_cache_create_usercopy() call)
Just set a minimum msize to 4k in both code paths, until someone complains they have a use-case for a smaller msize.
We need to check in both mount option and server reply individually because the msize for the first version request would be unchecked with just a global check on clnt->msize.
Link: http://lkml.kernel.org/r/1541407968-31350-1-git-send-email-asmadeus@codewrec... Reported-by: syzbot+0c1d61e4db7db94102ca@syzkaller.appspotmail.com Signed-off-by: Dominique Martinet dominique.martinet@cea.fr Cc: Eric Van Hensbergen ericvh@gmail.com Cc: Latchesar Ionkov lucho@ionkov.net Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/9p/client.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+)
--- a/net/9p/client.c +++ b/net/9p/client.c @@ -181,6 +181,12 @@ static int parse_opts(char *opts, struct ret = r; continue; } + if (option < 4096) { + p9_debug(P9_DEBUG_ERROR, + "msize should be at least 4k\n"); + ret = -EINVAL; + continue; + } clnt->msize = option; break; case Opt_trans: @@ -983,10 +989,18 @@ static int p9_client_version(struct p9_c else if (!strncmp(version, "9P2000", 6)) c->proto_version = p9_proto_legacy; else { + p9_debug(P9_DEBUG_ERROR, + "server returned an unknown version: %s\n", version); err = -EREMOTEIO; goto error; }
+ if (msize < 4096) { + p9_debug(P9_DEBUG_ERROR, + "server returned a msize < 4096: %d\n", msize); + err = -EREMOTEIO; + goto error; + } if (msize < c->msize) c->msize = msize;
@@ -1043,6 +1057,13 @@ struct p9_client *p9_client_create(const if (clnt->msize > clnt->trans_mod->maxsize) clnt->msize = clnt->trans_mod->maxsize;
+ if (clnt->msize < 4096) { + p9_debug(P9_DEBUG_ERROR, + "Please specify a msize of at least 4k\n"); + err = -EINVAL; + goto free_client; + } + err = p9_client_version(clnt); if (err) goto close_trans;